StringBuilder:ArrayIndexOutOfBoundsException [英] StringBuilder: ArrayIndexOutOfBoundsException

问题描述

我们在WebSphere 7/IBM JDK 6中遇到了一个奇怪的问题，其中一个节点存在一些初始化问题.

We're experiencing a strange issue with WebSphere 7/ IBM JDK 6, where one of the nodes has some initialization issue.

我们有一些调用InitialContext.lookup的代码，在此节点上，有时会出现以下异常:

We have some code which calls InitialContext.lookup and on this node we're getting sometimes the following exception:

Caused by: java.lang.ArrayIndexOutOfBoundsException
         at java.lang.String.getChars(String.java:666)
         at java.lang.StringBuilder.append(StringBuilder.java:207)
         at javax.naming.spi.NamingManager.getURLContext(NamingManager.java:646)
         at javax.naming.InitialContext.getURLOrDefaultInitCtx(InitialContext.java:422)
         at javax.naming.InitialContext.lookup(InitialContext.java:436)
         [...]

我们看了javax.naming.spi.NamingManager.getURLContext的源代码:

We had a look at the source code of javax.naming.spi.NamingManager.getURLContext:

public static Context getURLContext(String schema, Hashtable<?, ?> envmt)
        throws NamingException {

    if (null == schema || 0 == schema.length() || null == envmt) {
        return null;
    }

    // obtain pkg prefixes from hashtable
    String pkgPrefixes[] = EnvironmentReader
            .getFactoryNamesFromEnvironmentAndProviderResource(envmt, null,
                    Context.URL_PKG_PREFIXES);

    for (String element : pkgPrefixes) {
        // create factory instance
        ObjectFactory factory;
        String clsName = element + "." //$NON-NLS-1$
                + schema + "." //$NON-NLS-1$
                + schema + "URLContextFactory"; //$NON-NLS-1$
    [...]

第646行是增强的for循环，但是下一条语句是String串联，编译器可能会将其替换为StringBuilder.

Line 646 is the enhanced for-loop, but the next statement is a String concatenation and is probably replaced with a StringBuilder by the compiler.

我们在StringBuilder上进行了一些快速的单元测试，但无法引发ArrayIndexOutOfBoundsException.

We did some quick unit tests on StringBuilder but couldn't provoke an ArrayIndexOutOfBoundsException.

如何在这里抛出ArrayIndexOutOfBoundsException以及如何避免它?

How can an ArrayIndexOutOfBoundsException be thrown here and how can we avoid it?

修改:

我们正在使用以下Java版本:

We are using the following java version:

java version "1.6.0"
Java(TM) SE Runtime Environment (build pxa6460sr9fp2ifix-20110913_02(SR9 FP2+IV03622+IZ99243))
IBM J9 VM (build 2.4, JRE 1.6.0 IBM J9 2.4 Linux amd64-64 jvmxa6460sr9-20110912_90359 (JIT enabled, AOT enabled)
J9VM - 20110912_090359
JIT  - r9_20101028_17488ifx31
GC   - 20101027_AA)
JCL  - 20110727_04

推荐答案

这是IBM JVM的JIT编译器的已知错误.解决方法似乎是在JIT编译中排除了getChars:

This is a known bug of the JIT compiler of the IBM JVM. The workaround seems to be the exclusion of getChars from the JIT compilation:

-Xjit:exclude={ProgramClass.callStringGetChars*}

请参见 IZ78413:JIT兼容的字符串.GETCHARS抛出意外的ARRAYINDEXOUTOFBO UNDSEXCEPTION 供参考.

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